This application is a continuation of International Application No. PCT/JP99/04872, filed on Sep. 8, 1999, which claims the benefit of Japanese Patent Applications No. 10-254343, filed on Sep. 8, 1998 and No. 10-285763, filed on Oct. 7, 1998.
The present invention relates to an electron beam device and, more particularly, to an electron beam device having a spacer for maintaining the interval between an electron source and a member to be irradiated with electrons, a method for producing a charging-suppressing member used in the electron beam device, and an image forming apparatus.
Conventionally, electron-emitting elements are mainly classified into two types of elements: a thermionic cathode element and cold cathode element. Of these elements, the thermionic cathode element is used in a cathode ray tube and the like. Known examples of the cold cathode element are surface-conduction type electron-emitting elements, field emission type electron-emitting elements (to be referred to as FE type electron-emitting elements hereinafter), and metal/insulator/metal type electron-emitting elements (to be referred to as MIM type electron-emitting elements hereinafter).
The surface-conduction type electron-emitting element utilizes the phenomenon that electrons are emitted from a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction type electron-emitting element includes an electron-emitting element using an SnO2 thin film by Elinson [M. I. Elinson, Radio Eng. Electron Phys., 10, 1290, (1965)], an electron-emitting element using an Au thin film [G. D Mitter, xe2x80x9cThin Solid Filmsxe2x80x9d, 9,317 (1972)], an electron-emitting element using an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)], and an electron-emitting element using a carbon thin film [Hisashi Araki et al., Vacuum, Vol. 26, No. 1, 22 (1983)].
FIG. 24 is a plan view showing an element by M. Hartwell et al. described above as a typical example of the element structures of these surface-conduction type electron-emitting elements. In FIG. 24, reference numeral 1 denotes a substrate; and 2, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 2 has an H-shaped pattern, as shown in FIG. 24. The conductive thin film 2 undergoes electrification processing called electrification forming to form an electron-emitting portion 3.
In electrification forming, a constant DC voltage or a DC voltage which rises at a very low rate of, e.g., 1 V/min is applied between the two ends of the conductive thin film 2 to partially destroy or deform the conductive thin film 2, thereby forming the electron-emitting portion 3 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 2 forms a fissure. When an appropriate voltage is applied to the conductive thin film 2 after electrification forming, electrons are emitted by the electron-emitting portion 3 near the fissure.
After electrification forming processing, a voltage pulse is periodically applied in a vacuum atmosphere as electrification activation processing, thereby depositing on the electron-emitting portion 3 carbon or a carbon compound derived from an organic compound present in the vacuum atmosphere. This electrification activation processing enhances a stable electron emission effect.
Known examples of the FE type electron-emitting element are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField Emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical Properties of Thin-Film Field Emission cathodes with molybdenium Conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
FIG. 24 is a sectional view showing an element by C. A. Spindt et al. described above as a typical example of the element structure of the FE type electron-emitting element. In FIG. 24, reference numeral 4 denotes a substrate; 5, an emitter wiring line made of a conductive material; 6, an emitter cone made of molybdenum or the like; 7, an insulating layer; and 8, a gate electrode. This electron-emitting element emits electrons toward a high-voltage electrode arranged above the element by applying a proper voltage between the emitter cone 6 and the gate electrode 8, and emitting a field from the distal end of the emitter cone 6.
As another element structure of the FE type electron-emitting element, in addition to the stacked structure having a conical shape as shown in FIG. 24, an emitter and gate electrode are arranged on a substrate to be almost parallel to the substrate plane.
A known example of the MIM type electron-emitting element is described in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devices, J. Appl. Phys., 32,646 (1961). FIG. 25 shows a typical example of the element structure of the MIM type electron-emitting element. FIG. 25 is a sectional view. In FIG. 25, reference numeral 9 denotes a substrate; 10, a lower electrode made of a metal; 11, an insulating layer as thin as about 100 xc3x85; and 12, an upper electrode made of a metal with a thickness of about 80 to 300 xc3x85. The MIM type electron-emitting element emits electrons from the surface of the upper electrode 12 by applying a proper voltage between the upper electrode 12 and the lower electrode 10.
Compared to a thermionic cathode element, various cold cathode elements described above can emit electrons at a low temperature, and does not require any heater. Thus, the cold cathode element has a simpler structure than the thermionic cathode element, and can form a small element. Even if many elements are arranged on a substrate at a high density, problems such as thermal melting of the substrate hardly arise. In addition, the response speed of the thermionic cathode element is low because it operates upon heating by a heater, whereas the response speed of the cold cathode element is high.
As applications of cold cathode elements, there are image forming apparatuses such as an image display apparatus and image recording apparatus, charge beam sources, and the like.
Particularly as applications of cold cathode elements to an image display apparatus, as disclosed in U.S. Pat. No. 5,066,883 by the present applicant and Japanese Patent Application Laid-Open Nos. 2-257551 and 4-28137, an image display apparatus using a combination of a surface-conduction type electron-emitting element and a fluorescent substance which is irradiated with an electron beam to emit light has been studied. That is, there is an image display apparatus using a combination of a surface-conduction type electron-emitting element and a fluorescent substance which is irradiated with an electron beam to emit light has been studied.
A known application of FE type electron-emitting elements to an image display apparatus is a flat display apparatus reported by R. Meyer et al. [R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Micro-electronics Conf., Nagahama, pp. 6 to 9 (1991)].
An application of many MIM type electron-emitting elements arranged side by side to an image display apparatus is disclosed in Japanese Patent Application Laid-Open No. 3-55738 by the present applicant.
Of these electron-emitting elements, the surface-conduction type electron-emitting element has a simple structure and can be easily manufactured, and many elements can be easily formed in a wide area.
An image display apparatus using a combination of a surface-conduction type electron-emitting element and fluorescent substance is superior to a liquid crystal display apparatus in that the image display apparatus does not require any backlight because of self-emission type and that the view angle is wide.
In a flat image display apparatus, many electron-emitting elements are arranged on a flat substrate, and fluorescent substances for emitting light by electrons are arranged to face the electron-emitting elements. The electron-emitting elements are arrayed in a two-dimensional matrix (to be referred to as a multi electron source), and each element is connected to a row-direction wiring line and column-direction wiring line. An example of the image display method is the following simple matrix driving.
To emit electrons from an arbitrary row in the matrix, a selection voltage is applied in the row direction, and a signal voltage is applied to column wiring lines in synchronism with this.
Electrons emitted by the electron-emitting elements of the selected row are accelerated toward the fluorescent substances to excite the fluorescent substances and emit light. By sequentially applying the selection voltage in the row direction, an image is displayed.
The space between a substrate (rear plate) on which electron-emitting elements are formed in a two-dimensional matrix, and a substrate (face plate) on which fluorescent substances and an acceleration electrode are formed must be maintained in vacuum. Since the atmospheric pressure acts on the rear plate and face plate, the display apparatus requires a substrate thick enough to resist the atmospheric pressure as the display apparatus becomes bulky. However, this increases the weight. For this reason, the apparatus adopts a structure in which support members (spacers) are interposed between the rear plate and the face plate to keep the interval between the rear plate and the face plate constant and to prevent damage to the rear plate and face plate.
The spacer must have a mechanical strength enough to resist the atmospheric pressure, but does not greatly influence the orbit of electrons traveling between the rear plate and the face plate. The cause of influencing the electron orbit is charge of the spacer. The spacer is charged because some of electrons emitted by the electron source or secondary electrons reflected by the face plate are incident on the spacer, the spacer further emits secondary electrons, or ions ionized by collision of electrons attach to the surface.
If the spacer is positively charged, electrons traveling near the spacer are attracted to the spacer, and thus a display image is distorted near the spacer. The influence of charge becomes more typical as the interval between the rear plate and the face plate increases.
As a general means of suppressing charge, the charged surface is rendered conductive, and a small current is flowed to remove electric charges. A method of applying this concept to the spacer and covering the spacer surface with tin oxide is disclosed in Japanese Patent Application Laid-Open No. 57-118355. Japanese Patent Application Laid-Open No. 3-49135 discloses a method of covering the spacer surface with a PdO-based glass material.
High luminance is an important factor for the image display apparatus. To efficiently emit light from fluorescent substances formed on the face plate, the fluorescent substances are irradiated with electrons accelerated at a high voltage. To emit light with high efficiency, the height of the spacer is set to about 1 to 8 mm, and the acceleration electrode voltage is set to 3 kV or more, and desirably 5 kV or more. Therefore, a voltage of several kV or more is applied between the rear plate and the face plate, and a voltage of almost the same potential is applied across the spacer. The material used for the spacer is required not to discharge upon application of the acceleration voltage.
As a means of increasing the creeping discharge pressure resistance, the surface is effectively covered with a material having a low secondary electron emission ratio. Known examples of covering the surface with a material having a low secondary electron ratio use chromium oxide (T. S. Sudarshan and J. D. Cross: IEEE Tran. EI-11, 32 (1976)) and copper oxide (J. D. Cross and T. S sudarshan: IEEE Tran. EI-9146 (1974)).
As prior arts relating to the spacer, U.S. Pat. No. 5,598,056, U.S. Pat. No. 5,690,530, U.S. Pat. No. 5,561,340, U.S. Pat. No. 5,811,919, and EPA 1725418 are known.
As described above, spacers have been extensively developed to solve the functional problems relating to the spacers. The invention according to the present application has as its object to implement a suitable electron beam device using a developed spacer. In particular, it is another object of the invention to implement an arrangement capable of suppressing charge on a first member when a member such as a spacer is interposed between an electron source and a member to be irradiated with electrons in an electron beam device.
It is still another object of the present invention to implement an arrangement capable of desirably rendering at least a portion of the first member near the surface conductive when a member such as a spacer is interposed between an electron source and a member to be irradiated with electrons. It is still another object of the present invention to realize a spacer suitable for an image forming apparatus represented by an image display apparatus in which electrons emitted by an electron source are accelerated at a potential having a potential difference of 3 kV or more from the potential of the electron source, and the electrons cause fluorescent substances to emit light.
One invention of an electron beam device according to the present application has the following arrangement.
According to the present invention, an electron beam device having an electron source for emitting electrons, a member to be irradiated with the electrons, and a first member interposed between the electron source and the member to be irradiated is characterized in that a surface of the first member has a three-dimensional shape, and projecting portions of the three-dimensional shape form a network shape.
According to another invention of an electron beam device according to the present application, an electron beam device having an electron source for emitting electrons, a member to be irradiated with the electrons, and a first member interposed between the electron source and the member to be irradiated is characterized in that a surface of the first member has a three-dimensional shape, and the three-dimensional shape has recessed portions each continuously surrounded by projecting portions.
The three-dimensional shape is constituted by a film formed on a substrate of the first member. The three-dimensional shape may be constituted by a plurality of films formed on a substrate of the first member. The three-dimensional shape is constituted by a film formed on a substrate of the first member and a film from which part of an underlayer of the film is exposed.
The underlayer of the film from which part of the underlayer is exposed is preferably conductive. In particular, the underlayer preferably includes a conductive film formed on the substrate. The conduction is preferably semiconduction. Exposure of the underlayer means electronic exposure. More specifically, the underlayer is determined to be exposed when the structure of a spacer surface is evaluated as an evaluation means at an acceleration voltage of 1 kV and an incident angle of 75xc2x0 to confirm a crystal grain boundary, axiality, or the like that matches the structure of the underlayer (lower layer) on an SEM (Scanning Electron Microscope) image.
In an arrangement using the film from which part of the underlayer is exposed, the first member preferably has a 100 xcexcmxc3x97100 xcexcm-region in which a value obtained by dividing a covering area of the film from which part of the underlayer is exposed by an exposure area of the underlayer is not less than ⅓ and not more than 100. The first member preferably has a 100 xcexcmxc3x97100 xcexcm-region in which an average value of an area of each portion from which part of the underlayer is exposed is not more than 5,000 xcexcm2. The first member preferably has a 100 xcexcmxc3x97100 xcexcm-region in which an average value of a width of each portion from which part of the underlayer is exposed is not more than 70 xcexcm.
The film from which part of the underlayer is exposed may include an insulating film. When the underlayer is conductive, the film from which part of the underlayer is exposed need not be conductive even if the first member is to be rendered conductive to some degree. This increases the degree of freedom of choice of the material. The resistance value of the film from which part of the underlayer is exposed is a volume resistance of 104 xcexa9m or more to 108 xcexa9m or less.
Further, an arrangement can be adopted in which a secondary electron emission coefficient of the film from which part of the underlayer is exposed is smaller than a secondary electron emission coefficient of the underlayer. In the above invention, for example, the first member includes a spacer for maintaining an interval between the electron source and the member to be irradiated.
The above invention can be more preferably applied to a case wherein the first member includes a member arranged at a position which, when the first member is charged, substantially changes by charge an orbit of electrons emitted by the electron source.
A charging-suppressing member producing method which suppresses charge according to the present invention comprises the following invention as a method of manufacturing a member whose charge is suppressed. A charging-suppressing member producing method which particularly suppresses charge of a spacer is characterized by comprising the step of forming on a substrate a film from which part of an underlayer is exposed, the step comprising applying a material of the film in a liquid state.